Intervertebral disc disease and disc erosion as well as vertebral disease and vertebral deformity can cause severe back pain, and the typical pathophysiology of chronic back pain is a compression of a spinal nerve due to one of these spinal abnormalities.
When two vertebral bodies are separated by an eroded intervertebral disc, it can lead to a vertebral body collapsing onto the vertebral body directly below it. The collapse of the first vertebral body onto the second vertebral body deforms the vertebral anatomy, which can lead to a compression or pinching of a spinal nerve that can be exacerbated with motion.
The compression or pinching of a spinal nerve typically causes severe radiating pain down the distribution of the compressed or pinched nerve.
A typical surgical treatment for a compressed or pinched spinal nerve is a spinal fusion procedure. A spinal fusion procedure fuses two or more vertebrae together to eliminate the motion of these vertebrae, thus alleviating the nerve compression due to abnormal motion of the vertebrae.
A typical way to perform a spinal fusion procedure is by placing pedicle screws through the vertebral pedicles and into the vertebral bodies of two or more collapsed vertebra, and then attaching supporting bars to the pedicle screws. The supporting bars attached to the pedicle screws that are positioned within the vertebrae function similarly to scaffolding, connecting and fixing vertebrae together by fixing together pedicle screws embedded in the vertebrae.
A pedicle screw typically comprises a reticulating head referred to as a tulip. After the pedicle screw has been placed, a tulip may be used to align and secure a supporting bar that is coupled with that tulip. Once a desired position of a supporting bar is achieved a setscrew is used to fix the supporting bar to the tulip.
Torque applied to the pedicle screw and tulip setscrew to achieve proper placement and proper vertebral fixation is transferred to the vertebral pedicle and vertebral body. Too much torque applied to either the pedicle screw or tulip may fracture the vertebra through which a pedicle screw is placed or cause damage to the pedicle screw assembly.
Numerous other orthopedic procedures involve the placement of screws into bone, including, for example, bone fixation devices such as those used in long bone fracture reductions and fixations and in halos. Similar to vertebral fixation, too much torque applied when a screw is placed into a bone may cause fracture of the bone tissue or failure of the medical device.